Chabad – Yom Kippur commemorates the day when G‑d forgave the Jewish people for the sin of the Golden Calf. Forty days after hearing G‑d say at Mount Sinai, “You shall not have the gods of others in My presence; you shall not make for yourself a graven image,” the Jews committed the cardinal sin of idolatry. Moses spent nearly three months on top of the mountain pleading with G‑d for forgiveness, and on the tenth of Tishrei it was finally granted: “I have pardoned, as you have requested.”
From that moment on, this date, henceforth known as the Day of Atonement, is annually observed as a commemoration of our special relationship with G‑d, a relationship that is strong enough to survive any rocky bumps it might encounter. This is a day when we connect with the very essence of our being, which remains faithful to G‑d regardless of our outward behavior.